The present invention relates to a computer monitoring device which monitors whether a computer provided at a power window system of a vehicle or the like operates normally.
Conventionally, in a system using a microcomputer in which a battery is a power supply, when the microcomputer is not used, the microcomputer enters a standby mode and the execution of a program is stopped in order to reduce electricity consumption of the battery. Further, a microcomputer monitoring circuit (watchdog circuit) is provided in the system using the microcomputer. The microcomputer monitoring circuit monitors a state of the microcomputer by the output of a predetermined signal (e.g., a signal which is generated on the basis of a clock signal and will be hereinafter referred to as xe2x80x9cclock signalxe2x80x9d) from the microcomputer. When the clock signal is not detected, the microcomputer monitoring circuit determines that the state of the microcomputer is not normal and outputs a signal which restarts the microcomputer (hereinafter, xe2x80x9crestarting signalxe2x80x9d).
On the other hand, because the microcomputer stops the output of the above-described clock signal by entering the standby mode, the microcomputer monitoring circuit outputs the restarting signal. As a result, the microcomputer which is supposed to enter the standby mode is restarted.
In order to prevent the restarting of the microcomputer which is supposed to enter the standby mode, when the microcomputer monitoring circuit detects a signal which is output when the microcomputer enters the standby mode (hereinafter, xe2x80x9cstandby signalxe2x80x9d), the microcomputer monitoring circuit also enters the standby mode. Namely, when the standby signal is detected, the microcomputer monitoring circuit enters the standby mode and stops the monitoring function of the microcomputer.
An example of a system which includes the microcomputer and the microcomputer monitoring circuit is a power window system of a vehicle. In this power window system, a microcomputer controls a relay or the like and operates a motor for raising and lowering a door glass in accordance with a switch operation. At this time, a microcomputer monitoring circuit monitors an operating state of the microcomputer in order to prevent the control of the motor from being disabled due to runaway or the like of the microcomputer. When it is determined that the microcomputer does not operate normally, a restarting signal is output to the microcomputer.
On the other hand, the power window system includes a microcomputer control system and an SW control system (direct control by a switch) so as to control the motor in accordance with the switch operation. The motor is usually controlled by the microcomputer control system. When the microcomputer enters the standby mode or it is determined by the operating state of the microcomputer monitoring circuit that the operation of the microcomputer fails, the motor is controlled by the SW control system. In this way, the motor can be controlled even if the microcomputer does not operate normally.
By the way, when a microcomputer port or an input terminal of the microcomputer monitoring circuit fails, the standby signal may be input to the microcomputer monitoring circuit by mistake. In this case, even when the microcomputer becomes abnormal and the restarting signal is output, since the microcomputer monitoring circuit detects the standby signal, the microcomputer monitoring circuit enters the standby mode and stops monitoring of the microcomputer which is a fundamental function.
In order to prevent this, a microcomputer monitoring circuit has been proposed which, when a restarting signal is output, does not enter a standby mode even if a standby signal is detected, and which can monitor the microcomputer even if the microcomputer is started in a state in which a wrong standby signal is detected. When this microcomputer monitoring circuit detects a reset signal which is output from a watchdog circuit at the time of starting the microcomputer and thereafter detects a standby signal before detecting a clock signal, the microcomputer monitoring circuit ignores the standby signal and monitors the microcomputer on the basis of the clock signal.
However, if the microcomputer operates properly even if a state of the microcomputer cannot be monitored properly, the above-described microcomputer monitoring circuit continuously monitors the microcomputer. As a result, when, for example, the microcomputer enters the standby mode and the clock signal is stopped, a drawback arises in that the microcomputer is restarted.
The present invention was developed in light of the above circumstances, and the object thereof is to provide a computer monitoring device which monitors a microcomputer only when a state of the microcomputer can be monitored properly.
In order to solve the above-described problems, the present invention comprising: starting means which outputs a starting signal before starting a computer, the starting means outputting a starting signal to the computer when a first signal, which is output from the started computer in a predetermined cycle, is stopped for a predetermined period of time; start stopping means which stops an operation of the starting means when a second signal, which is output from the computer with a predetermined timing, is input; signal output means which outputs a first signal, which is output from the microcomputer in a state in which the second signal is not detected, to the starting means; start operation determination means which outputs a third signal, which urges stopping of the operation of the start stopping means, due to inputting of the starting signal, the start operation determination means stopping outputting of the third signal when the first signal is output from the signal output means; and operation monitoring means which stops outputting of the input second signal to the start stopping means when the start operation determination means outputs the third signal.
In accordance with the present invention, the starting means outputs the starting signal after a predetermined time has passed since the first signal, which is output from the computer in a predetermined cycle, is not input. Further, when the second signal, which is output from the computer at the time of entering the standby mode, is detected, the start stopping means stops the operation of the starting means.
On the other hand, the first signal is input to the starting means via the signal output means. When the signal output means detects the second signal, the first signal is not output to the starting means even if the first signal is input.
Further, the start operation determination means outputs the third signal due to the input of the starting signal and stops the output of this third signal by the first signal output from the signal output means. The operation monitoring means outputs this second signal to the start stopping means due to the detection of the second signal and stops the output of the second signal to the start stopping means when the third signal is detected.
As a result, when the second signal is input by mistake at the time in which the computer is started by the starting signal output from the starting means, the third signal is output from the start determination means and the output of the second signal to the starting means is stopped. Further, since the signal output means does not output the first signal to the starting means, the starting means outputs the starting signal at predetermined time intervals. Consequently, the computer is started by the starting signal input in succession.
In this way, because the computer is started every time the starting signal is output at predetermined time intervals when the second signal is input by mistake, the computer cannot be operated. Accordingly, the computer is not started in a state in which the computer cannot be monitored properly. In other words, the computer cannot be started in a state in which the computer cannot be monitored properly.
In the present invention, when the start operation determination means outputs the third signal, it can be determined if the computer operates properly or if the operation of the computer can be managed properly. The state in which the microcomputer operates can be monitored (determined) from the output of the start operation determination means and the operation monitoring means.
Therefore, when the present invention is applied, for example, to monitor the computer of the power window system, only when the second signal or the third signal is not detected, it can be determined that the computer operates normally. Thus, switching between the microcomputer control system and the SW control system may be effected on the basis of this result of determination.